Since the near universal entitlement for dialysis services in 1972, the U.S. end-stage renal disease (ESRD) program has grown to more than 150,000 individuals representing expenditures in excess of 3 billion, annually. Financial incentives for dialysis providers have stimulated the development and maintenance dialyzer reprocessing programs in the vast majority of U.S. dialysis facilities. Despite the extensive diffusion of this technology, our understanding of the long-term health effects of this practice is incomplete. Most concerning are accumulating data that dialyzer reprocessing, as it is currently practiced in the U.S. today, may be associated with an important amount of excess morbidity among ESRD patients. The risks of infection and inadequate dialysis have been incompletely studied. Many studies of dialyzer reuse are inadequately controlled and most fail to adjust for the varied comorbidity among ESRD patients initiating dialysis. We propose to carry out an historical cohort study of the health effects of dialyzer reprocessing using a near random sample of U.S. hemodialysis patients for whom extensive comorbidity data are available. Patients dialyzed in units practicing dialyzer reprocessing will be compared to patients in units discarding dialyzers after each use with respect to overall survival and hospitalization-free survival. Multivariate survival analysis will permit the assessment of the health impact of dialyzer reuse while adjusting for the potentially confounding influence of baseline comorbidity. Although it is often difficult to examine the outcomes of established practices like dialyzer reuse, it is imperative that we conduct studies such as the one proposed here so that we can better make rational decisions regarding the rightful place of this technique in the care of ESRD patients.